The invention relates to a method for obtaining transfer characteristics of a device under test (DUT) as a function of frequency, the method comprising the steps of:
(1) applying a sine sweep x.sub.1 [n] to an input of the DUT, with n designating a time index; PA1 (2) measuring a response signal y.sub.1 [n] at an output of the DUT PA1 (3) applying a cosine sweep x.sub.2 [n] to an input of the DUT; PA1 (4) measuring a response signal y.sub.2 [n] at the output of the DUT. PA1 (1) a waveform generator arranged to provide an input of the DUT with a concatenation of a sine sweep and a cosine sweep; PA1 (2) a digital signal processing means arranged for analyzing a response signal of the DUT. PA1 (1) the IC comprises control circuitry for in a test mode controlling the waveform generator and the digital signal processing means; PA1 (2) the waveform generator is arranged for in the test mode providing an input of the subcircuit with a concatenation of a sine sweep and a cosine sweep; PA1 (3) the digital signal processing means is arranged for in the test mode analyzing a response signal of the subcircuit.
The invention further relates to an arrangement for obtaining transfer characteristics of a DUT as a function of frequency. The invention further relates to an integrated circuit (IC) comprising a waveform generator, a digital signal processing means and a subcircuit with transfer characteristics to be tested.
A method as specified in the preamble is known from article "DSP synthesized signal source for analog testing stimulus and new test method", H. Kitayoshi et al., International Test Conference 1985 Proceedings, IEEE Computer Society Press, November 1985. In the known method, an input signal in the form of a sine sweep (also `swept sine` or `frequency-swept sinewave`) is applied to an analog DUT and a response signal of the DUT is measured. Subsequently, a transfer function of the DUT is estimated with the aid of a frequency domain analysis of the input signal and the response signal. For both the construction of the input signal and the postprocessing a digital signal processor (DSP) is used.
DSPs offer a lot of possibilities with respect to both the generation of input stimuli and the postprocessing of the obtained response signals. Of course, when the DUT has an analog input and/or an analog output, as for instance with an analog filter or a digital-to-analog converter (DAC), separate DACs and/or analog-to-digital converters (ADCs) are required in a test environment in which the method is applied, in order to be able to use a DSP for signal generation and/or postprocessing. In order to maintain clarity of the text, we will only describe digital signals being applied to and obtained from the DUT, whereas it is silently understood that, if necessary, appropriate conversions for interfacing with the DUT take place.
A sine sweep is a sinusoidal signal with a varying instantaneous frequency. Sine sweeps have the advantage over other input stimuli, like multi-tone signals, that they not only have a low crest factor, but in addition are robust with respect to non-linear phase changes and can be easily adapted to cover a particular frequency range of interest.
A prerequisite of the known method is that a Fourier transformation needs to be applied to the input signal and to the response signal. Fourier transformations are time-consuming and put a burden on test system resources.